PubMed · 2615959
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G Kh Merzhanova, A I Berg. Cortico-hypothalamic interneuronal correlation during learning in cats.. https://doi.org/10.1007/bf01181860
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Ischemic preconditioning (PC) of heart and brain is a well-documented phenomenon. However, the mechanism underlying the increased resistance to severe ischemia by a preceding mild ischemic exposure remains unclear. Over a decade ago, we demonstrated the existence of hypoxic PC in the hippocampal slice preparation. Here we report the ability of a short exposure to toxic levels of glutamate to heighten the tolerance of hippocampal slices to a subsequent, longer exposure to the excitotoxin. Glutamate PC could also be induced by a short hypoxic exposure, suggesting a common mechanistic pathway for all PC stimuli. Since glutamate receptor activation and hypoxia increase tissue lactate production, a-cyano-4-hydroxycinnamate was applied during the PC period to completely abolished PC. These results indicate that excitotoxic PC and hypoxic PC share similar mechanisms that possibly involve lactate production and its neuronal utilization.
Extracellular single-unit activity was recorded from subfornical organ (SFO) neurons antidromically identified as projecting to the hypothalamic paraventricular nucleus (PVN) in urethane-anesthetized ovariectomized female rats that were treated with either propylene glycol (PG) vehicle or estradiol benzoate (EB). No significant differences were observed between the PG- and EB-treated rats in the latency, conduction velocity, or threshold of antidromic activation. The mean spontaneous firing rate was significantly lower and the refractory period was significantly longer in the EB-treated rats. In the identified units that were activated by angiotensin II (ANG II) applied iontophoretically, the amount of excitatory response to intracarotid administration of ANG II was much greater in the PG-treated than in the EB-treated rats. These results suggest that estrogen may decrease the responsiveness of SFO neurons projecting to the PVN to circulating ANG II.
The role of dopamine (DA) on motor cortical pyramidal tract neurons (PTNs) was studied in anesthetized cats with in vivo extracellular recordings in response to transcallosal (TC) and ventrolateral (VL) thalamic stimulations. An antidromic PT potential was evoked to recognize PTNs. In most PTNs, iontophoretic application of DA significantly reduced the spike activity exerted by 20 single-pulse stimulations. Both D(1)-like and D(2)-like receptor antagonists blocked (disinhibited) the effect in a similar way regardless of TC and VL stimulations, suggesting colocalization of two receptors. Except for the presence of jittering, the mean latency was usually fixed and short. These findings indicate that ventral midbrain DA imposes an intense suppression in modulating PTNs response to both callosal and thalamocortical excitatory inputs in motor cortex. Such DAergic suppression could play pivotal role to improve motor and sensorimotor signal integration.